1. Field of the Invention
The present invention relates to a method for setting recording power for a multilayer optical recording medium, the multilayer optical recording medium, and a method for recording information on the multilayer optical recording medium.
2. Description of the Related Art
Conventionally, optical recording media such as CD-DA, CD-ROM, CD-R, CD-RW, DVD-ROM, DVD-R, DVD+/-RW, and DVD-RAM have been widely used to view digital moving image contents and record digital data. In the meantime, optical recording media of these types have been demanding greater recording capacity year after year. To meet this demand, commercialization has started of so-called next-generation DVDs which are capable of recording a large volume of moving images or data. For increased recording capacity, the next-generation DVDs use laser light having a wavelength as short as 405 nm for recording and reading.
For example, the Blu-ray Disc (BD) standard, one of the next-generation DVD standards, makes it possible to record and read up to 25 GB on a single recording layer, with an objective lens of 0.85 in numerical aperture.
The sizes of moving images and data are expected to grow more and more in the future. As described in nonpatent document, K. Mishima et. al., Proc. of SPIE, 6282, 628201 (2006), there have thus been proposed technologies pertaining to a so-called multilayer optical recording medium in which recording layers are increased in number so as to increase the capacity of the optical recording medium. For BD-based multilayer optical recording media, some techniques have been proposed to achieve an ultra high capacity of 200 GB through the provision of six to eight recording layers.
When information recording layer in a multilayer medium is irradiated with laser light for recording, the amount of light to reach the information recording layer to be recorded depend on the recording states of information on the other information recording layers through which the laser light passes. The inventor's study, which is yet publicly unknown as of the filing of the present application, has revealed the following. Depending on difference in the transmittances of the information recording layers for the laser light to pass through, the proportion of the recording laser light to reach the intended information recording layer can differ by 10% or more, with an adverse effect on the recording quality of the information recording layer. In particular, there has been found the problem that the information recording layer farthest from a light incident surface can produce recording errors easily due to the foregoing transmittance difference since it must be irradiated with the laser light through all the other information recording layers.